#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
sRGB Colourspace
================
Defines *sRGB* colourspace opto-electrical transfer function (OETF / OECF) and
electro-optical transfer function (EOTF / EOCF):
- :func:`oetf_sRGB`
- :func:`eotf_sRGB`
See Also
--------
`RGB Colourspaces IPython Notebook
<http://nbviewer.jupyter.org/github/colour-science/colour-notebooks/\
blob/master/notebooks/models/rgb.ipynb>`_
References
----------
.. [1] International Electrotechnical Commission. (1999). IEC 61966-2-1:1999 -
Multimedia systems and equipment - Colour measurement and management -
Part 2-1: Colour management - Default RGB colour space - sRGB, 51.
Retrieved from https://webstore.iec.ch/publication/6169
.. [2] International Telecommunication Union. (2015). Recommendation
ITU-R BT.709-6 - Parameter values for the HDTV standards for
production and international programme exchange BT Series Broadcasting
service (Vol. 5). Retrieved from https://www.itu.int/dms_pubrec/\
itu-r/rec/bt/R-REC-BT.709-6-201506-I!!PDF-E.pdf
"""
from __future__ import division, unicode_literals
import numpy as np
from colour.utilities import as_numeric, warning
__author__ = 'Colour Developers'
__copyright__ = 'Copyright (C) 2013-2016 - Colour Developers'
__license__ = 'New BSD License - http://opensource.org/licenses/BSD-3-Clause'
__maintainer__ = 'Colour Developers'
__email__ = 'colour-science@googlegroups.com'
__status__ = 'Production'
__all__ = ['oetf_sRGB',
'eotf_sRGB']
[docs]def oetf_sRGB(L):
"""
Defines the *sRGB* colourspace opto-electronic transfer function
(OETF / OECF).
Parameters
----------
L : numeric or array_like
*Luminance* :math:`L` of the image.
Returns
-------
numeric or ndarray
Corresponding electrical signal :math:`V`.
Examples
--------
>>> oetf_sRGB(0.18) # doctest: +ELLIPSIS
0.4613561...
"""
L = np.asarray(L)
return as_numeric(np.where(L <= 0.0031308,
L * 12.92,
1.055 * (L ** (1 / 2.4)) - 0.055))
[docs]def eotf_sRGB(V):
"""
Defines the *sRGB* colourspace electro-optical transfer function
(EOTF / EOCF).
Parameters
----------
V : numeric or array_like
Electrical signal :math:`V`..
Returns
-------
numeric or ndarray
Corresponding *luminance* :math:`L` of the image.
Examples
--------
>>> eotf_sRGB(0.461356129500442) # doctest: +ELLIPSIS
0.1...
"""
warning(('*sRGB* *OETF* is a piece-wise function: in order to reduce '
'noise in dark region, a line segment limits the slope of the '
'power function (slope of a power function is infinite at zero). '
'This is not needed for *sRGB* *EOTF*, a pure gamma 2.2 function '
'should be use instead. This definition is used for symmetry in '
'unit tests and others computations but should not be used as an '
'*EOTF*!'))
V = np.asarray(V)
return as_numeric(np.where(V <= oetf_sRGB(0.0031308),
V / 12.92,
((V + 0.055) / 1.055) ** 2.4))